Theory with spoilers (of sorts)
Knowing the nature of Stargate and it's time bending stories, could one surmise that:
The Destiny Crew who created the Novus people who branch out to other worlds eventually get get caught in some kind of battle (maybe with the drones or the obelisk aliens) and travel back in time so far (perphaps trying to dial earth again) that they end up back on earth and use the destiny as a failsafe (it does seem to be on some kind of course correction) essentially becoming the Ancients themselves.
Hope that makes sense.